(568ac) Modeling of Alternatives for Recovering the Exhaust Heat from a Gas Turbine Power Plant of Ecopetrol

The current electrical energy demand in GEC-Ecopetrol is 200 MW and an increase of about 240 MW is expected in the next 10 years for new oil wells and enhanced oil recovery. To satisfy part of this new demand, GEC-Ecopetrol is planning to improve the efficiency of the existing power generation facilities and to use a new natural gas source that has become available in Termosuria, one of the main GEC-Ecopetrol power plants. Currently, Termosuria has a gas turbine producing between 34 - 37 MW by a simple Brayton cycle. However, gas turbines in simple cycle are limited by their thermal efficiency, achieving up to 40%. The main energy loss in gas turbines is the heat contained in the exhaust gases, which have a temperature of 840°F in Termosuria. This stream can be used to generate more power by adding a steam Rankine cycle to the process. Generally, the implementation of this combined cycle (CC) results in up to 60% global efficiency increase.    

In this paper, two design alternatives of a new combined cycle are modeled for the Termosuria GE LM6000® gas turbine. Since the Heat Recovery Steam Generator (HRSG) is one of the few non-standardized components of the combined cycle that can be customized, both alternatives are focused on the HRSG design, specifically in the implementation, or not, of a post-combustion burner. The influence of environmental conditions (temperature and humidity) on plant performance is studied by applying a typical daily variation curve, obtained from a monitoring meteorological tower installed near the plant site. The thermodynamic behavior is modeled in Gate Cycle® software and the economic analysis is modeled in VBA-Excel®; both models are integrated by CycleLink® utility. For each alternative, the following indicators of plant performance are calculated, hour by hour, following a typical daily curve of environmental conditions:  Generated power, thermal efficiency and cost of electricity (COE).